Double Glazed units in timber frames

[Giff]

I am making some inward opening (french style) DG windows to replace some older single glazed units of similar construction. I have only ever made SG frames before. Can anyone tell me how to bed in / seal DG units into the frame. Thanks G

 

[davem62]

Hi
My older double glazed Windows were bedded with Butyl putty and I've just double glazed my garage / workshop window frames with Geocel glazing silicone after speaking to their tech dept that it doesn't affect the sealed unit bonding
Regards David

 

[Steve Maskery]

The way you install the units can have an enormous effect on their longevity.

You should ensure that the edges of the unit do not touch the wooden frame at any point That means an air gap underneath, above and up both sides.

The frame's rebate should be properly painted prior to fitting the glass.

The air gap around the unit should be ventilated. This can be achieved by having the bottom retaining bead leave an air gap underneath.

Butyl putty is a good choice, as is glazing silicone or glazing tape, but not ordinary silicone or linseed oil putty.

There is an excellent treatise on designing wooden DG windows. I forget the author, Hislop or Hiscox or something like that, but I'll have a hunt. I have it but I think it is on a machine I rarely use. If I find it I'll get back to you.

 

[Giff]

Thanks David for that recommendation.

Steve I think I have just found the book on Amazon. Is it Wood Windows: Designing for High Performance by Patrick Hislop ?

Great thanks Geoff

 

[RossJarvis]

The way you install the units can have an enormous effect on their longevity.

You should ensure that the edges of the unit do not touch the wooden frame at any point That means an air gap underneath, above and up both sides.

The frame's rebate should be properly painted prior to fitting the glass.

The air gap around the unit should be ventilated. This can be achieved by having the bottom retaining bead leave an air gap underneath.

Butyl putty is a good choice, as is glazing silicone or glazing tape, but not ordinary silicone or linseed oil putty.

There is an excellent treatise on designing wooden DG windows. I forget the author, Hislop or Hiscox or something like that, but I'll have a hunt. I have it but I think it is on a machine I rarely use. If I find it I'll get back to you.

+1 for the above. Additionally I think it's at least a good idea, if not essential to have drainage as well, such as a hole drilled from the bottom of the air gap/s ending up at the bottom of the door. You usually see this in UPVC frames.

 

[Steve Maskery]

Here we are:

High performance wood windows
Patrick Hislop BA (Hons Arch) RIBA, TRADA Technology Ltd

It used to be a free document, now it is a paid-for book, Heigh ho. Not cheap, but then it is a very specialist publication. The document is excellent, though, so I would expect the book to be worth the price.

Unless you find it on Abebooks! That puts the TRADA price into context...

 

[Steve Maskery]

Ross, drainage, yes. That is what I meant by having an air gap underneath the bottom retaining bead. If the bottom rail of the casement is bevelled, and air can get in to ventilate it, it stays dry and doesn't rot the wood nor cause the unit seal to fail. Water is our enemy.

The design in Hislop is excellent. I used it on my last house and the results were excellent (although I wasn't there long enough to report long-term) but when I explained to the glazier how I was making them, he said (If I were making windows for my own house, that's how I would do them". Good enough for me.

 

[RobinBHM]

Usually double glazed units are made with the spacer set back 12mm from the edge of the glass, so that is what needs to line up with the edge of the rebate.

There should be an air gap ideally 5mm, so the glazing rebate should be a minimum of 16mm for a 4mm gap or up to 18mm for a 6mm gap.

Use glazing shims the same thickness as the glass, ie a 24mm wide shim for 24mm glass so the bottom of both panes is supported.

We machine in a 10mm wide x 6mm deep groove in the bottom rebate and then drill a 8mm hole from this to the bottom of the sash close to the front.

There are differences of opinion regarding glazing, we use wet glazing with neutral cure silicone. do not fill the air gap just close it off with a 6mm dia bead before fitting the glazing bead, assuming external beading, if internal beading then a different method applies.

 

[Giff]

Thanks for the replies.Here is a Sketchup. Do I have to leave a gap all round the DG unit so it stands off the timber ? These are inward opening so does the front rebate / moulding need to be siliconed as well ?

 

[katellwood]

just my two penneth

My frames are Iroko made with 1/2" rebates and fitted with 4-12-4 double glazed units beaded on the outside.

The units were fitted with clear glazing silicone, a bead of silicone along the back of the rebate prior to fitting the unit, then a bead of silicone along the back of the glazing bead prior to fixing If i recall correctly initially i did also silicone around the edge of the glazing unit in effect fully sealing the whole unit (this was done on approx three casements until I was advised otherwise)

the whole lot has been in for over twenty years and never a problem, no leaks, no misting. In addition they are leaded on the outer glass panel on both sides of the glass. this has also stayed intact

In essence they are as good today as the day they were fitted

If i were doing them today I would fit them in a 15mm rebate but basically use the same technique

Don't know about painted softwood/accoya units as I hate paint and try to avoid it whenever I can

 

[Fitzroy]

Just made mine fully bedded. ie the same as katellwood's. Mine are however beaded on the exterior face, but not sure that really matters. The key idea with a fully bedded system is that there is no path for water to enter the cavity around the DGU.

As with many of my choices history will be the judge. katellwood's solution was the same as mine so hopefully my execution will be as good as his was and I'll duplicate his 20yr experience.

F.

 

[HOJ]

In my case, I follow the Glass unit manufacturers instructions, which if followed, will comply with the warranty scheme they offer.

 

[Jake]

Where I have glazed my own I have fully bedded with MSP. No problems so far.

The ventilated and drained system sounds great until some insects/dirt etc get in and block the hole which won't take long. Nice in theory but doesn't seem wholly practical to me.

 

[Steve Maskery]

What Hislop is advocating is not a drainage hole, it is a wholly vented bottom strip, which in turn access the sides and top. The sealed unit is, in effect, floating in mid-air, with only the faces of the glass in contact with anything at all.

I am intrigued by the fully bedded idea though. It does make a lot of sense, I just wonder why he doesn't advocate it. It seems more obvious. I'll see if I can sit and read it all again, I've not had cause to do so for a long time.

 

[ColeyS1]

Where I have glazed my own I have fully bedded with MSP. No problems so far.

The ventilated and drained system sounds great until some insects/dirt etc get in and block the hole which won't take long. Nice in theory but doesn't seem wholly practical to me.

I use to hate machining the bottom bead for that system ! It seemed like such a faff.
I think completely sealed is better. I've made hundreds of windows this way and can only think of one unit that failed prematurely, after being hit with a football. I think that pane lasted a good 10 years

Coley

 

[Giff]

Thanks for the replies, the fully bedded method does seem the best so far though.
The windows will be inward opening and will have a drain / gutter arrangement at the bottom ( Macclesfield Step ?). The ones I am replacing have an aluminium one so the water drains down and out of these as a front / back door may do.I have made a similar window in the past and machined a V gutter, with angled holes into the sill, as I had seen in France.
Steve I have order the Hislop book and it is arriving tomorrow so I will look at that as well.

 

[Doug71]

I generally fully seal my units.

Packers under and round edge of unit, min 3mm gap, silicone round the edge of unit (make sure you use the proper stuff that is suitable for use near the edge of double glazed units not just a glazing silicone), butyl tape between rebate and glass, and glass and bead. Pin beads in with stainless steel pins.

This is when the beads are external, if internal glazed I might go for the drained method as using the above method the silicone would be at the back instead of the front.

Doug

 

[RossJarvis]

I've just remembered that I'm doing a porch after Christmas, which will be made up of Seasoned oak posts and "beams" about 4" x 4", on a brick dwarf wall to about 3' - 4'. My intention is to use beads either side of the dg units and not into rebates. I'm presuming with this, the butyl strip should take the movement of the wood over time and need to ensure the units aren't "clamped" in between any spacers, so essentially floating.

Anyone done this sort of thing?

Cheers

 

[Giff]

I bought the Patrick Hislop book......expensive ! Here is a drawing I have done. Are there any flaws or problems that any experienced people can help with or advise. It is a Stormguard weather strip and I have use their drawing and built round it. Thanks Geoff

 

[HappyHacker]

Over 30 years ago when I fitted double glazing to my existing house I used softwood frames, all I could afford, and used butyl putty to fully seal the units in the frame. It was about 10 years before they started blowing. The butyl went as hard as a rock although I had been told it would never set. The replacement double glazing I put in lasted longer but I had put drain holes in and supported the glass on packers. Now, I am sorry to say, replaced with plastic.